nuclear physics institute, academy of sciences of the czech republic
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Studies of neutron cross-sections by activation method in Nuclear Physics Institute Řež and in The
Svedberg Laboratory Uppsala and experimental determination of neutron production in spallation
reactions
Nuclear Physics Institute, Academy of Sciences of the Czech RepublicDzelepov Laboratory of Nuclear Problems, Joint Institute for Nuclear Research, RussiaDepartment of Nuclear Reactors, Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague
Varna, BulgariaVarna, Bulgaria 16.-22.9.201316.-22.9.2013
J. Vrzalová, O. Svoboda, A. Kugler, M. Suchopár, V. Wagner
collaboration Energy and Transmutation of Radioactive Waste
vrzalova@ujf.cas.cz
2
Introduction The collaboration Energy and Transmutation of
Radioactive Waste use different setups consisting of lead, natural uranium and graphite irradiated by relativistic protons and deuterons to study transmutation of radioactive materials by produced neutrons.
Activation samples are used to determine production of neutron flux in different places of experimental set-ups.
Unfortunately, the cross-sections of many reactions important for our activation detectors are missing.
To improve situation, we studied the neutron cross-sections using different quasi-monoenergetic neutron sources based on proton reaction on 7Li target in NPI Řež and in The Svedberg Laboratory Uppsala.
- Motivation
- Cross - section measurements
- Neutron sources
- Background subtraction
- NPI Řež
- TSL Uppsala
- Comparison NPI, TSL
- Conclusion
3
Outline- Motivation
- Cross - section measurements
- Neutron sources
- Background subtraction
- NPI Řež
- TSL Uppsala
- Comparison NPI, TSL
- Conclusion
Motivation Cross-section measurements Neutron sources in NPI and TSL Background subtraction Experiments on cyclotron in Řež TSL Uppsala experiments Comparison Conclusion
4
Motivation- Motivation• Evaluation• Corrections
- Cross - section measurements
- Neutron sources
- Background subtraction
- NPI Řež
- TSL Uppsala
- Comparison NPI, TSL
- Conclusion
dEEENbeam
thresh
E
E
yield )()(
we measured threshold reactions on Au, Al, Bi, In, Ta, Ti, Y commonly used for such purposes and we also studied other materials: Cu, Fe, I, Mg, Ni, Zn.
evaluated from the experimentevaluated from the experiment
we would like to findwe would like to find!!
poor poor knowledgeknowledge, , we want to we want to measuremeasure
Solving a Fredholm equation we can find Φ(E):
the spatial distribution of neutron field inside ADS-setup can be determined with the help of Fredholm equation
due to poor knowledge for us imported neutron cross-section we carried out series of experiments devoted to their determination
5
Evaluation process-Motivation• Evaluation• Corrections
- Cross - section measurements
- Neutron sources
- Background subtraction
- NPI Řež
- TSL Uppsala
- Comparison NPI, TSL
- Conclusion
BACKGROUNDBACKGROUND
SUBTRACTIONSUBTRACTION
209Bi(n,4n)206Bi
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
24 29 34 39 44 49 54 59 64 69 74 79 84 89 94
Neutron energy [MeV]
Cro
ss s
ect
ion
[ba
rn]
EXFOR TALYS 1.4. NPI Řež TSL Uppsala
6
Spectroscopic corrections
- Motivation• Evaluation• Corrections
- Cross - section measurements
- Neutron sources
- Background subtraction
- NPI Řež
- TSL Uppsala
- Comparison NPI, TSL
- Conclusion
Self-absorption
Detector efficiency
Correction for real coincidences
Square-emitter corection
Dead time correction
Decay during cooling
Decay during irradiation
Unstable irradiation 0,88
0,90
0,92
0,94
0,96
0,98
1,00
0 5 10 15 20
Distance from sample to detector [cm]
Squ
are-
emitt
er c
orre
ctio
n [-
]
1.25x1.25 cm
2x2 cm2.5x2.5 cm
3x3 cmiodine 3cm round
Uncertainty caused by the corrections was estimated to be less than 1% in total, except the uncertainty from efficiency calibration of the detector, which is below 3 %.
7
Evaluation - total yield- Motivation• Evaluation• Corrections
- Cross - section measurements
- Neutron sources
- Background subtraction
- NPI Řež
- TSL Uppsala
- Comparison NPI, TSL
- Conclusion
)()(
)(
11
1
)(
)( 0
irrreal tirr
t
t
foillive
real
areaP
aabspyield e
t
e
e
mt
t
CCoiEI
BECSN
Peak area Self-absorption correction
Beam correction
Dead time correction
Decay during cooling and measurement
γ line intensity
Detector efficiency
Correction for coincidences
Square-emitter correction
Weight
normalization
Decay during
irradiation
8
Cross-section measurements
- Motivation• Evaluation• Corrections
- Cross - section measurements
- Neutron sources
- Background subtraction
- NPI Řež
- TSL Uppsala
- Comparison NPI, TSL
- Conclusion
Requirements for -measurements by activation method:
high energy neutron source with good intensity
monoenergetic (quasi-monoenergetic) neutrons or well known spectrum
pure monoisotopic samples
good spectroscopic equipment – and X-rays detectors
Then we can calculate Nyield and finally :An
yield
NN
ASN
Number of neutrons
in peak
foil size relative mass
Avogadro´s
number
9
- Motivation• Evaluation• Corrections
- Cross - section measurements
- Neutron sources
- Background subtraction
- NPI Řež
- TSL Uppsala
- Comparison NPI, Uppsala
- Conclusion
Neutron sources NPI ASCR Řež: Energy range 14 – 37 MeV, neutron intensity ~ 108 n.cm-2.s-1
TSL Uppsala: Energy range 20 – 180 MeV, neutron intensity ~ 105 n.cm-2. s-1
0.0E+00
2.0E+14
4.0E+14
6.0E+14
8.0E+14
1.0E+15
1.2E+15
4 9 14 19 24 29 34 39
Neutron energy [MeV]
Num
ber
of n
eutr
ons
(1/s
r M
eV C
)
E=25 MeV
E=20 MeV
E=32.5 MeV
E=37 MeV
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 10 20 30 40 50 60 70 80 90 100
Neutron energy [MeV]
Neu
tron
flux
[1/M
eV (p
eak
area
= 1
)]
E = 50 MeV p-beam
E = 62 MeV p-beam
E = 70 MeV p-beam
E = 80 MeV p-beam
E = 92 MeV p-beam
E = 97 MeV p-beam
1E0
1E2
1E4
1E6
1E8
1E-7 1E-5 1E-3 1E-1 1E+1 1E+3Neutron Energy [MeV]
Neu
tro
n f
lux
den
sity
[1/
(cm
2.s)
]
spallation source at JINR
quasi-monoenergetic source at TSL102
104
108
106
0 10-7 10-3 10-5
10-1 101 103
Neutron spectra comparison
10
- Motivation• Evaluation• Corrections
- Cross - section measurements
- Neutron sources
- Background subtraction
- NPI Řež
- TSL Uppsala
- Comparison NPI, TSL
- Conclusion
Background subtraction
background contribution was determined by folding of the neutron source spectrum and calculated cross-sections (TALYS 1.4)
we calculated ratio between production in neutron peak and total production and with this ratio we multiplied the yields to subtract background production
0
1
15 35 55 75 95Energy [MeV]
Cro
ss-s
ectio
n v
ers
us n
eu
tro
n s
pe
ctr
um
[-]
Bi-204
beam 50 MeV(0.99)beam 62 MeV(0.87)beam 70 MeV(0.57)beam 80 MeV(0.40)beam 92 MeV(0.29)beam 97 MeV(0.28)
11
- Motivation• Evaluation• Corrections
- Cross - section measurements
- Neutron sources
- Background subtraction
- NPI Řež
- TSL Uppsala
- Comparison NPI, TSL
- Conclusion
Uncertainty analysis HPGe detector calibration uncertainty: less than 3%
Gauss-fit of the gamma peaks: > 1% (usually less than 10%)
spectroscopic corrections uncertainty: less than 1%
neutron spectra determination: 10%
neutron beam intensity determination: 10%
uncertainty of background subtraction: 10% in the worst case (big background, big model influence)
12
- Motivation• Evaluation• Corrections
- Cross - section measurements
- Neutron sources
- Background subtraction
- NPI Řež
- TSL Uppsala
- Comparison NPI, TSL
- Conclusion
Experiments in NPI four measurements
proton beam energies 20, 25, 32.5 and 37 MeV
irradiation time about 20 h.,irradiated foils: Ni, Zn, Bi, Cu, In, Al, Au, Ta, Fe and I
the sample distances from the lithium target – from 11 cm to 16 cm
13
- Motivation• Evaluation• Corrections
- Cross - section measurements
- Neutron sources
- Background subtraction
- NPI Řež
- TSL Uppsala
- Comparison NPI, TSL
- Conclusion
Experiments in TSL proton beam energies 50, 62, 70, 80, and 92 and 97 MeV
irradiation time about 8 h
14
- Motivation• Evaluation• Corrections
- Cross - section measurements
- Neutron sources
- Background subtraction
- NPI Řež
- TSL Uppsala
- Comparison NPI, TSL
- Conclusion
NPI and TSL resultsComparison of cross-sections (n,xn) reactions on natural indium with TALYS
15
- Motivation• Evaluation• Corrections
- Cross - section measurements
- Neutron sources
- Background subtraction
- NPI Řež
- TSL Uppsala
- Comparison NPI, TSL
- Conclusion
Comparison of cross-sections (n,xn) reactions on iodine and tantalum with EXFOR, TALYS and libraries of evaluated data
16
- Motivation• Evaluation• Corrections
- Cross - section measurements
- Neutron sources
- Background subtraction
- NPI Řež
- TSL Uppsala
- Comparison NPI, TSL
- Conclusion
Comparison of cross-sections (n,x) reactions on aluminium and yttrium with TALYS, EXFOR and libraries of evaluated data
17
- Motivation• Evaluation• Corrections
- Cross - section measurements
- Neutron sources
- Background subtraction
- NPI Řež
- TSL Uppsala
- Comparison NPI, TSL
- Conclusion
Also with the help of our measured cross-section we can analyze neutron flux in different places of experimental set-ups consisting of lead, natural uranium and graphite irradiated by relativistic protons and deuterons (for example QUINTA – more about this setup in the talk of Mr. Furman or Mr. Wagner).
- neutron flux determined with the help of method “effective cross-sections” (experiment at phasotron in JINR Dubna – 660MeV protons, massive lead target, threshold detectors were situated on the target surface).
18
- Motivation• Evaluation• Corrections
- Cross - section measurements
- Neutron sources
- Background subtraction
- NPI Řež
- TSL Uppsala
- Comparison NPI, TSL
- Conclusion
Conclusion ten cross-section measurements were carried out in NPI Řež and in
TSL Uppsala
energy region from 17 MeV to 94 MeV was covered
we studied various materials in the form of thin foils and observed good
agreement with the data in EXFOR database and also with the cross-
sections calculated in deterministic code TALYS.
with the help of neutron cross-section we can analyze
neutron flux in different places of experimental set-ups
all our observed reactions you can find in journal: Nuclear Instruments
and Methods in Physics Research - Vol.726, (2013) 84-90
some of our results are already included in EFXOR
19
Thank you!supervisor in NPI Řež: RNDr. Vladimír Wagner, CSc.
supervisor in JINR Dubna: prom. fyz. Jindřich Adam, CSc.
wagner@ujf.cas.cz
iadam@jinr.ru
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